With the
advantage of low readout noise and high-speed readout, CMOS technology has
revolutionized astronomical imaging. A monochrome, back-illuminated,
high-sensitivity, astronomical imaging camera is the ideal choice for
astro-imagers.
The QHY600 uses the latest SONY
back-illuminated sensor, the IMX455, a full frame (35mm format) sensor with
3.76um pixels and native 16-bit A/D. This sensor is available in both
monochrome and color versions. The QHY600 ends the days of non-16bit CMOS
cameras and it ends the days non-full frame (and larger) monochrome CMOS
cameras.
Equipped
with a Sony IMX455, the QHY600 is a back-illuminated Scientific CMOS Camera
with extremely low dark current (0.002e/p/[email protected]) using SONY’s Exmor BSI CMOS
technology. QHY600 is also a zero amplifer glow camera.
The
QHY600 has only one electron of read noise at high gain and full resolution and
4FPS readout speed. One electron of read noise means the camera can
achieve a SNR>3 at only 4 to 6 photons. This is perfect performance when
conditions are photon limited, i.e., short exposures, narrow band imaging,
etc., making this large area sensor ideal for sky surveys, time domain
astronomy, fluorescence imaging, DNA sequencing and microscopy.
2GB
DDR3 image buffer
In
order to provide smooth uninterrupted data transfer of the entire 60MP sensor
at high speed, the QHY600 has 2GB DDR3 image buffer. The pixel count of the
latest generation of CMOS sensors is very high resulting in greater memory
requirements for temporary and permanent storage. For example, the QHY600
sensor produces about 120MB of data per frame. The data band-width is
also increased from the original 16-bits to the current 32-bits.
Transferring such a large file sizes necessarily requires the camera to have
sufficient memory. The QHY600 has adopted a large-capacity memory of up to
2GB. Data throughput is doubled. This large image buffer meets the needs
of high-speed image acquisition and transmission of the new generation of CMOS,
making shooting of multiple frames smoother and less stuttered, further
reducing the pressure on the computer CPU.
Another
advantage is that when using some computers that do not have fast processors or
have poor support for USB 3.0, the computer can’t transfer high-speed data
well, and the data is often lost. The DDR can buffer a lot of image data and
send it to the computer. Even if the USB 3.0 transmission frequently gets
suspended, it will ensure that data is not lost. There are options in SharpCap
to turn DDR buffering on or off. The current version of the ASCOM driver works
in DDR mode.
Extended Full Well Capacity and
Multiple Read Modes
With
a pixel size of 3.76um, these sensors already have an impressive full well
capacity of 51ke. Nevertheless, QHYCCD has implemented a unique approach
to achieve a full well capacity higher than 51ke- through innovative user
controllable read mode settings. In extended full well readout mode, the
QHY600 can achieve an extremely large full-well charge value of nearly 80ke- and
the QHY268C can achieve nearly 75ke-. Greater full-well capacity provides
greater dynamic range and large variations in magnitude of brightness are less
likely to saturate. The QHY600 / 268C have three readout modes with
different characteristics.
Native
16 bit A/D: The new Sony sensor has native 16-bit A/D
on-chip. The output is real 16-bits with 65536
levels. Compared to 12-bit and 14-bit A/D, a 16-bit A/D yields
higher sample resolution and the system gain will be less than 1e-/ADU with no
sample error noise and very low read noise.
BSI: One
benefit of the back-illuminated CMOS structure is improved full well capacity.
This is particularly helpful for sensors with small pixels. In a typical
front-illuminated sensor, photons from the target entering the photosensitive
layer of the sensor must first pass through the metal wiring that is embedded
just above the photosensitive layer. The wiring structure reflects some of the
photons and reduces the efficiency of the sensor. In the back- illuminated
sensor the light is allowed to enter the photosensitive surface from the
reverse side. In this case the sensor’s embedded wiring structure is below the
photosensitive layer. As a result, more incoming photons strike the photosensitive
layer and more electrons are generated and captured in the pixel well. This
ratio of photon to electron production is called quantum efficiency. The higher
the quantum efficiency the more efficient the sensor is at converting photons
to electrons and hence the more sensitive the sensor is to capturing an image
of something dim.
Zero
Amplify Glow: This is also a zero amplifier glow camera.
TRUE
RAW Data: In the DSLR implementation there is a RAW image output, but
typically it is not completely RAW. Some evidence of noise reduction and
hot pixel removal is still visible on close inspection. This can have a
negative effect on the image for astronomy such as the “star eater”
effect. However, QHY Cameras offer TRUE RAW IMAGE OUTPUT and
produces an image comprised of the original signal only, thereby maintaining
the maximum flexibility for post-acquisition astronomical image processing
programs and other scientific imaging applications.
Anti-Dew
Technology: Based on almost 20-year cooled camera design
experience, The QHY cooled camera has implemented the fully dew control
solutions. The optic window has built-in dew heater and the chamber is
protected from internal humidity condensation. An electric heating board for
the chamber window can prevent the formation of dew and the sensor itself is
kept dry with our silicon gel tube socket design for control of humidity within
the sensor chamber.
Cooling: In
addition to dual stage TE cooling, QHYCCD implements proprietary technology in
hardware to control the dark current noise.
